This invention relates to a circuit arrangement for use in combination with an amplifier for amplifying an input signal sent from a satellite or the like.
An amplifier of the type described comprises an active element, such as a field effect transistor or the like, and an input circuit, namely, a circuit arrangement for delivering an input signal to the active element. Inasmuch as the amplifier is supplied with an extremely weak radio wave from a satellite, generation of noise should be reduced in the amplifier per se as low as possible. Effective reduction of the noise in the amplifier is possible by lowering loss in the circuit arrangement, as known in the art.
For this purpose, an isolator is used in the circuit arrangement. A matching circuit should, however, be connected between the isolator and the active element to match impedances between the isolator and the active element. The amplifier therefore is disadvantageous in that the noise characteristic is inevitably degraded by connection of the matching circuit. In addition, connection of the matching circuit makes the amplifier bulky.